Atara Biotherapeutics, Inc.

As previously disclosed, on March 23, 2026, a putative shareholder class action captionedKuang v. Atara Biotherapeutics, Inc., et al., No. 2:26-cv-03083 (the “Class Action”), was filed in the U.S. District Court for the Central District of California (the “Court”) against the Company and certain of its current and former officers (collectively, “Defendants”). On June 11, 2026, the Court issued an order appointing a lead plaintiff (the “Lead Plaintiff”), and on August 10, 2026, the Lead Plaintiff filed an Amended Class Action Complaint. The amended complaint purports to assert claims under Sections 10(b) and 20(a) of the Securities Exchange Act of 1934 and SEC Rule 10b-5 promulgated thereunder on behalf of purchasers or acquirers of the Company’s securities from May 20, 2024 through January 9, 2026. The complaint alleges, among other things, that Defendants made materially false or misleading statements and omissions regarding alleged deficiencies in the Company’s Phase 3 ALLELE study of tabelecleucel for the treatment of Epstein-Barr virus-positive post-transplant lymphoproliferative disease, and the likelihood of FDA approval and regulatory prospects for the Company’s Biologics License Application for tabelecleucel. Defendants have filed a motion to dismiss the complaint. The Company believes that the allegations are without merit and intends to vigorously defend against them.